While there have been many designs for vehicles which can be substantially converted in appearance or function from automotive fashion to airplane fashion, they have failed to become successful products in the commercial market. This is usually a direct result of the various conflicting requirements that arise when one attempts to combine these two types of vehicles. The previous inventors have typically focused on addressing one or more of these conflicts but have not fully resolved all issues in order to provide for a practical vehicle in both modes. In some other cases the resulting combination vehicle is either too complex or impractical for commercial acceptance.
One problem with prior art devices is that they fail to adequately provide a manner in which to deal with the wings when transitioning from airplane mode to highway mode. Many past designs have provided wings that can be folded. Multiple joints or complex folding mechanisms of prior art devices typically add too much weight or cost to the vehicle. In some cases stowage schemes compromise aesthetics, or highway aerodynamics excessively. In other cases wing design for aircraft mode is compromised yielding unacceptable flying qualities. U.S. Pat. Nos. 4,986,493 and 4,579,297 are examples of vehicles that have wing folding means which are too complex to be practical. In a preferred embodiment, wing folding is accomplished easily with actuators.
A second problem found in prior art devices is inadequate propulsion of the vehicle in each mode. Simplified designs have proposed using aerodynamic thrust to propel the vehicle in both modes. For example, U.S. Pat. No. 2,674,422 provides a vehicle that proposes using aerodynamic thrust for automotive propulsion. This is a big problem on public highways, however, because excessive noise and foreign object entrainment result. An alternative is to drive one or more wheels with the same engine that drives the propeller, which has also been done but the transmission systems proposed have not produced good results. It is well known that drive wheels must support a substantial vehicle mass fraction in order to provide sufficient traction. This requirement, when applied to aircraft, causes another conflict. In order for a conventional aircraft to have acceptable take-off and landing qualities the center of gravity must be located very close to the main load bearing wheels. When the center of gravity is placed near one or more wheels (as is the case in prior art devices), unacceptable tipping resistance occurs for accelerations associated with highway operation.
What is needed is a practical roadable aircraft.